Airplane propeller



Dec. 7, 1937.

E. MARTIN AIRPLANE PROPELLER Filed May 7, 1954 2' Sheets-Sheet 1 Dec. '7, 1931. E. MARTIN 1 2,101,149

AIRPLANE PRQPELLER Filed Ma 1954 ZSheejs-Sheet 2 IN VEN TOR.

Erik. M11121 A TTORNEY Patented Dec. 7, 1937' PATENT OFFICE AIRPLANE PROPELLER Eric Martin, Emmi-a, Conn, assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application May 7, 1934, Serial No. 724,418

8 Claims.

Airplane propellers may be made hollow and of metal and the present invention is particularly adapted to such propellers although in all of its aspects it may not be confined thereto.

Such airplane propellers are subjected to large stresses when operated. A purpose of the present invention is to secure a better distribution of such stresses and to reinforce the parts particularly affected. The invention also has to do with mounting blades of airplane propellers in their hubs. Other phases of the invention are important in the manufacture of the blades.

} In the accompanying drawings Figure 1 is a plan view of an airplane hub carrying two propeller blades which are illustrated broken oif, the right hand portion of the figure being illustrated in horizontal section. Fig. 2 is a transverse vertical section on the line 2'-2 of Fig. 1. Figure 3 is a schematic illustration showing a furnace and a die press used in the within described process of manufacturing airplane propellers. Figure 4 is a vertical sectional view on an enlarged scale of the front end of the die press illustrated in Figure 3 showing a propeller blank and reinforcing sleeve in. position in the dies. Figure 5 is a vertical sectional view similar to Figure 4, illustrating a subsequent stage in the operation of the die press.

In the drawings is illustrated a shaft III which may be rotated by the motor or in any desired way. Mounted on the shaft I0 is a split hub consisting of the inner section I l and the outer section l2 held together by means of the bolts l3 passing through lugs l4 carried by the two sections of the hub H and I2. The hub sections comprise inner thimble members l5 which may close-'- ly surround the. shaft l0. On their outer surfaces the-hub sections ll and l2 include semi-circular slots it which cooperate with'each other to form circular cavities for holding the propeller blades ii. The propeller blades. ll illustrated consist of a hollow shell of metal, such as steel for instance', which tapers in thickness from the butt end toward the tip (not shown) At the hub end the blade is circular in cross section. It will be understood that the outer portion of the blade not here illustrated may be of any usual or desired airfoil form.

Within the butt end of the propeller blade I1 is a sleeve or thimble l8, preferably of such a metal as steel which, as illustrated, tapers in thickness in thesame direction as the wall of the blade and has at its.butt end an outwardly extending flange l9 which overlies and is in close contact with the out-turned flange 20 at the butt end of the blade H. The outer face 2| of the flange it may be (Cl. tail-156.8)

carefully machined smooth to rest upon and engage the correspondingly prepared seat 22 in the circular channel l6 of the hub members II and 12. It will be noted that the flange 20 of the blade I! extends at substantially right angles to the 5 main body of the blade I! but on its outer side instead of having a sharp right angle, it is formed with an easy curve indicated at 23. Likewise the turn at the inner edge of the flange 20, indicated at 24,is an easy curve corresponding'to the con- 10 tour of the sleeve l8. Resting against the curved portion 23 of the flange 20 of the blade I1 is a thrust ring 25 having an inner face 26 curved on a relatively large radius so as to have a relatively large surface seating on the flange 20. The curve 15 at 26 is preferably not identical with the curve at 23 and may be ona smaller radius so that there may be freedom to allow the parts under deforming forces to adjust themselves to fit. The thrust ring 25 as clearly indicated in Fig. '2, consists of two semi-circular members whose added circumference is slightly less than the outer circumference of the blank of the propeller blade H. The propeller blade ll, carrying the sleeve It, may be placed between the expanded hub members ll 25 and I2 with the seat 2| of the flange IS in position to rest upon the seat 22. The sections of the thrustring 25 may. then be placed in position about the base end of the blade I! and arranged against the outer surface 23 of the flange 20. The 30 sections I i and i2 of the hub may then be forced together so that the thrust ring- 25 is engaged by the circumference 21 of the cavity l6 and also by the inwardly extending lip 28. The bolts l3 may then be put in place and the sections II and i2 35 of the hub drawn tightly together and the thrust ring 25 will thus be forced against the flange-2ll of the propeller on an adjustable broad surface and so will force the flange l9 tightly against its, seat 22. The propeller blades I! will thus be 40 mounted by their respective flanges in the hub.

It will be noted that the outer circumferential surface of the flange 20 is held out of contact with the surface 21 of the cavity l6 and the lip 28 does not make contact'with the surface of the propeller 5 blade l'l.

- The thrust ring 25 may be made of steel and, as formed, permits the use of a very large fillet between the shank of the blade ll and the flange 20 and thus greatly improves the distribution of the 5 loads at this point. Although the surface 23 of the propeller blade at the flange end and the coacting surface 26 of the thrust ring are preferably of slightly difierent radii and might theoretically have only a line contact, the surface deflection at these points is great enough so that a substantial surface is in contact and the loads are not transmitted through a line contact.

In order to insure that the separation points 29 between the ends of the halves of the thrust ring do not coincide with the split between the two sections of the hub ii and W, in one or both of the halves of the thrust ring 25 there may be provided one or more holes or slots 30 to be engaged by positioning pin 3i placed in a corresponding slot 32 formed in one of the hub section's i ll adjacent its edge. Since the slot 30 in the thrust ring 25 is placed at some distance from the end of the is desirable that the tube be of as thin metal as possible. The operations to which the tube is submitted in the manufacture require that the inner diameter at the hub be kept substantially as large as any other point. It is obvious then that the tube cannot be thickened inwardly at the hub end. Likewise the hub end cannot be made very thi k outwardly. By beginning with a thick tube much material will be wasted, it may be nearly impossible to satisfactorily form the flange l and the possibility of procuring a tube of metal of uniform condition will be materially limited. Moreover, a very thick portion of the tube will be very dimcult to handle and properly heat treat. Nevertheless since the stresses on the blades inducedbythe whirling of the propeller in operation, are of very large magnitude some means of reinforcing the hub end of the'hollow blade are desirable. This is conveniently accomplished by providing the internal sleeve 98 which itself is tapered so as to provide the necessary reinforcing support progressively along the hub end of the blade. The blade is thus strengthened and the load distributed. Additional reinforcing metal on the surface of the shank of the blade may be undesirable as adding additional weight to the propeller because of the larger diameter on which the metal would occur. In manufacture the hollow tube H to form the propeller blade ll may be provided with a suitable flange and brought into the proper condition and then heated to a forging heat in a suitable furnace 32, a heat of from 1200 F. to 1700 F. being satisfactory for one material mentioned in the Squires application referred to. The tube may then be inserted into dies to deform the outer portion of the blade to proper airfoil shape. In the shaping operation the blank I1 is heated in the furnace 32 to a forging temperature, that is, a temperature at which the material of the blank may be deformed to the extent required without creating undue stresses in the material. When the blank is at the proper temperature, it is removed from the furnace and inserted in the die press 34, the press being in the position illustrated inFigure 3 with the upper and lower die members 36 and 38 respectively separated to their fullest extent. The blank is inserted through a ring member 40 supported upon the base of the die press and the blank is supported by the ring member so that it is out of contact with both die members, Immedie.

aromas diately after the blank is placed in the ring member 30, the sleeve i8 is inserted in place in the butt end of the blank and the breech member 412 is closed and locked in position against the adja cent face of the sleeve member thus rigidly securing the tube blank and sleeve member in the ring ill. As soon as the breech member 32 has been located in the closed position, illustrated in Figure 5, the upper and lower die members 36 and 38 are brought together to form the tube blank H to the proper air foil contour. As explained above the water cooled die elements 36 and 38 quickly remove the heat from all of the thin portions of the blade in contact with the .die members, but the mounting ring 60 is not capable of removing the heat from the thick root portion of the blade as rapidly as the heat is removed from the thinner portions by the water cooled die members. Under these conditions the insertion of the cold sleeve member it in the root or base end of the blade during the chilling proc- 'ess materially assists in providing all portions of the blade with the same temperature since the sleeve member removes the heat from the inside of the thickened base portion at the same time that the ring member ill and the adjacent end portions of the die members 36 and 38 are removing the heat from the thickened base portion through the exterior surface thereof. The condition thus described is clearly illustrated in Figure 5. The die members 36 and 38 are desirably provided with suitable cooling means such as the passages i l through which a cooling liquid may be forced to carry away the heat transferred to the die members by the hot blank ll. By means of this arrangement, the hot blank is quenched by the die to provide a heat treatment commonly referred to as chilling. In the above describedshaping operation the inner or hub end of the blade is not deformed, but it does undergo a heat treatment from its contact with the die member and ring 60. It is desirable that the metal of the propeller blade be all chilled or cooled to about the same metallurgical efiect. Since the hub end of the blade blank is thicker than the rest of the blade this portion will contain more heat units and will not be cooled as rapidly as the inner portions ofthe blade in contact with the Under these conditions, a uniform heat treatment of the entire blade may be conveniently accomplished by thrusting the sleeve l8 while cold into the heated hollow end of the blank l'l while in the dies for forming the outer portion of the blade. The putting in place of the cold sleeve l8 chills, from the inner side, the hub'end of the blade I! the outer side of which may be cooled by contact with the dies, and the flange l9, by contact with the flange 20, similarly chills or cools the flange 20. This procedure greatly improves the heat treatment of the blade end over any heat treatment that could be given to a solid hub end of equal strength, and this is done without actually increasing the thickness of the blade itselfself and, at the same time, reinforces the blade at the hub end. The length of the sleeve 18 and its proportions may vary in accordance with the desires of the designer or the results to be obtained.

The sleeve l8 may be made somewhat larger in diameter than the internal diameter of the hub end of the blade I I when cold. When heated to the forging temperature described above the blade 11 expands allowing the sleeve to be inserted and the cooling causes the sleeve l8 to have a shrink fit in the hub end of the blade. It

' a cold steel sleeve and cooling the surface of the appears, however, that there is a slight movement between the blade and the insert during operation and this movement absorbs energy and dissipates, in the form of heat, the energy which might otherwise cause undesirable stresses in the blade.

The invention has to do with the hub end of the propeller blade and the character of the outer portion of the blade is not of great importance to most phases of the invention. 'While the outer portion of the blade may be hollow some phases of the invention may be applied to a solid blade or to one which is substantially solid except for the hub end which may be hollow for a portion of the blade.

While there has been illustrated and described a suitable mechanical embodiment of a propeller blade constructed according'to the idea of the invention and a suitable process for manufacturing the improved blade, it is to be understood that the invention is not limited to the construction so illustrated and described nor to the particular steps of the process in the order hereinabove set forth but that such changes in the size, shape, and arrangement of parts and in the order of the steps of the process and in the various steps themselves may be resorted to as come within the scope of the appended claims.

Having described theinvention so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows.

I claim as my invention:

1. The method of heat treating a metal propeller blade blank having a thickened hollow end comprising heating the blank to a tempering heat, and inserting in the thickened hollow end blank in dies.

2. The method .of heat treating a metal propeller blade blank having a thickened hollow end with an outwardly extending flange comprising heating the blank to a forging heat, inserting in the end a cold steel sleeve having an outwardly extending flange so that the sleeve comes into close contact with and cools the contacting portion of. the blank and the flange on the sleeve comes into close contact with and cools the flange on the blank, and cooling the surface of p the blank in dies. 1

3. A metal propeller blade having a hollow hub with an outwardly extending flange and a portion adjacent the flange of varying wall thickness progressively decreasing away from the flange, and a reinforcing steel sleeve permanently secured within the end of the propeller blade by a shrink flt and having at its end an outwardlyv extending-flange in contact with the propeller flange and a body of exterior diameter a-pproxiinately equal to .the inside diameter of the propeller and having a wall of. varying thickness progressively decreasing away'from the flange.

4. An airplane propeller blade, an outwardly extending flange at the hub end so formed that the Junction between blade and flange on its outer face is a curve of relatively large diameter,

a split thrust ring surrounding the blade and having a face of corresponding curve engaging the junction of flange and blade and having a relatively flat outer face, a hub for supporting the blade, and a member engaging the flat face of the thrust ring and adapted by means of a radial movement to put pressure on the thrust ring to tend to hold the blade toward its seat.

5. An airplane propeller blade having a hollow hub end, an outwardly extending flange at the hub end having a flat face at the base of the blade and having a junction between theblade and flange in a curve of relatively large diameter, a reinforcing tubular insert in the blade and having an outwardly extending flange engaging the blade flange and having a flat face, a split thrust ring surrounding the blade and having a correspondingly formed face engaging the junction of the flange and blade and a flat face toward the blade tip, a split hub having a seat against which rests the flat face of the flange of the insert and a seat for the flat face of the thrust ring and means for contracting, the split hub in a direction radial of the propeller blade so as to cause the thrust ring to force the fiat face of the insert firmly against its seat.

6.- The method of manufacturing a metal pro-' peller blade which comprises forming a blank having a hollow thickened end portion with an outwardly extending flange, heating the blank to a tempering heat, rapidly removing the heat from the blank by placing the same in contact with a die, and at the same time removing heat the hollow end portion to act as a reinforcing sleeve in the end portion in contact with its inner surface, and leaving the sleeve in the hollow end portion of the blank to act as a reinforcing member for the flanged end portion of the blade.

8. The method of heat-treating a metal propeller blade blank having a hollow end which comprises, heating the blank to a heat-treating temperature, removing heat from the outside of said blade blank by placing it in contact with a solid cooling medium and simultaneously removing' heat from the inside of the hollow end of said blade blank by placing a cold sleeve in contact with the inside of said hollow end. 

